Mr. Q
The FBI intelligence bulletin from the bureau's Phoenix field office, dated May 30, 2019, describes "conspiracy theory-driven domestic extremists," as a growing threat, and notes that it is the first such report to do so. It lists a number of arrests, including some that haven't been publicized, related to violent incidents motivated by fringe beliefs.
The document specifically mentions QAnon, a shadowy network that believes in a deep state conspiracy against President Trump, and Pizzagate, the theory that a pedophile ring including Clinton associates was being run out of the basement of a Washington, D.C., pizza restaurant (which didn't actually have a basement).